Melting magnesium



Patented 12,.

ammo MAGNESIUM Russell and William 0. Binder, Niagara Falls, N. Y.,assignors to Electro Metallurgical Company, acorporation of WestVirginia No'Drawing. Application December a, 1943,

Serial No. 513,460

8 Claims. This invention relates to the melting of magnesium andmagnesium-base alloys and refers more particularly to containers forholding such materials in the molten condition.

A disadvantage of magnesium and its alloys which has hindered their useas structural materials for some purposes is their susceptibility tolocalized corrosion, generally believed to be due to impurities.Impurities are ordinarily introduced during melting operations in themanufacture of magnesium alloys or in the fabrication of useful articlesfrom magnesium and its alloys. The impurities thought to have the mostdamaging effect on the corrosion resistance of magnesium alloys are ironand nickel.

It is the commercial practice to employ carbon steel containers forhandling and holding molten magnesium and magnesium-base alloys duringtheir manufacture or fabrication. It has been observed that magnesiumand magnesium-base alloys so handled may have quite poor resistance tocorrosion despite the fact thatmagnesium of materials which include thestep of conducting such operations in containers composed of suchsteels.

The composition of the steel used for containem for molteni magnesiumand its alloys in accordance with the invention may vary widely withinthe composition limits given. For example, containers may be composed ofa steel containing 10% to manganese and 0.8% to 1.5% carbon. If a steelcontaining more manganese, say about 16% to is used, the car- 'boncontent is preferably diminished and. should very high purity is used,but no commercially ments in the method of melting magnesium andmagnesium-base alloys and in methods of handling such materials in themolten. condition.

The invention by which these objects are achieved is based on thediscovery that molten magnesium and its alloys may be held in contactwith certain steels, the principal characteristic of which is a highmanganese, content, without seriously detrimentally affecting theirresistance to corrosion. The invention comprises a container for moltenmagnesium and magnesium alloys, which container is composed of asteel-containing 10% to 30% manganese, the principal part of theremainder being iron. The steel of which the container of the inventionis composed preferably also contains up to 18% chromium and may containup to about 2% orsomewhat more silicon, up to 1.5% carbon, up to 2%columbium, up to 1% copper, up to 2% molybdenum, up to 3% nickel, and upto about 0.3% nitrogen, and the incidental impurities commonly presentin steels of good quality. The invention also comprises the improvedmethods of melting magnot be more than about 0.5%. For containers moreresistant to oxidation and loss of toughness at the elevatedtemperatures at which they are used, a steel containing up to 18%chromium, preferably 5% to 15% chromium, may be used. The presence ofcolumbium up to about 2% or molybdenum up to about 2%, or both, improvesthe high temperature strength of the steel. Preferably, not more than 1%each of columbium 'or molybdenum is present, and steels containing theseelements should contain less than 0.3% carbon. Small quantities ofcopper and of nickel may be present but the nickel content should notexceed about 3% nor the copper about 1%. Nitrogen in an amount notexceeding about 0.3% and preferably 0.05% to 0.15%, may be present inall of these steels as may be silicon, but the silicon content ispreferably under 2%.

The corrosion-resistance of magnesium which has been melted incontainers fabricated from the steels just described is markedlysuperior to the corrosion-resistance of magnesium, otherwise identical,which has been melted in containers composed of ordinary carbon steels.This conclusion is supported by the results of nu- 1 merous tests inwhich several different samples of commercially pure magnesium weremelted in different containers embodying theinvention and in carbonsteel containers under comparable melting conditions. Cast samples ofthe magnesium melted in these containers were subjected to corrosiontests in which the samples were exposed alternately to a 3% sodiumchloride solution for a few minutes and to air for a few minutes, thealternate exposures being repeated and continued for a period of severaldays. In general, samples produced from the first one or two batches ofmagnesium melted in a given conftainer had poor corrosion-resistance,but -samples produced from successive batches melted in the samecontainers had markedly improved ourrosion-resistance-except in the caseof samplesproduced from metal which had been melted in carbon steelcontainers. Typical test results are showninthe followingtableinwhichthecorrosion rate of samples taken from successive batchesof pure magnesium melted in containers having the composition indicatedis expressed as loss of weight in milligrams per squarecentimeterperday.

tlooi aluminum: m l a ubs tanfiyaillron) number mm Mplapess-ll l Theimproved corrosion-resistance oi substantially pure magnesium melted inthe containers of the invention, as compared with that of the samematerial melted in .carbon steel containers is evident from the abovetable. Similar resultswere obtained in tests conducted using several ofthe well known magnesium alloys now in commercial use containingmanganese and aluminum. some with and some without zinc, such alloysexhibiting substantially the same order of improvementincorrosion-resistance when melted in the containers of the invention asthat shown by the substantially pure magnesium.

To attain the benefits of theinvention, containers composed of the steeldescribed should be employed whenever magnesium and its alloys aremelted or are handled in the molten condition. By melting such materialsand by handlingv canon and a' more viscous flux for others. Thecontainers of the invention may be used for aw typeot melting procedure,with or without flux. In

the melting operations reported in ythe above table, a viscous fluxcontaining about potassium chloride, 21% magnesium chloride, 19% calciumchloride, 12% magnesium fluoride, 7%

calcium fluoride and 7% chloride was I used.

We claim:

$1. In the art of handling molten magnesi and magnesimn-base alloys, theimprovement which comprises holding such moltenmaterials in a containermade of steel containing 10% to 30% manganese.

2. In the art of melting magnesium and magnesium-base alloys, theimprovement which comprises melting such materials in a containercomposed oi a steel containing 10% to 30% manganese.

3. In the artoi melting magnesium and magnesium-base alloys, theimprovement which comprises melting such materialsin a containercomposed of a steel containing 10% to 30% manganese and up to about 18%.chromium.

4. In the art of melting ium and magneslum-base alloys, the improvementwhich comprises melting such materials in a container compom of asteelcontaining 10% to '25 manganese, 12% to 15% chromium, up to about2% each of columbium and silicon, up to about 1% of copper, up to about2% of molybdenum, carbon in an amount not exceeding about 0.3%,

the remainder substantially all iron.

5. A container for use in contact with molten magnesium andmagnesium-base alloys which container is composed of a steel containingabout 10% 'to 30% manganese.

6; A container for use in contact with molte magnesium andmagnesium-base alloys which container is composed of a'steel cents-lo n!about them. in the molten condition exclusively in such containers, theproduction of magnesium and magnesium-base alloys having greatlyimproved resistance to corrosion is achieved without changingsubstantially the composition of the materials now used commercially.

It is common practice in melting um and its alloys to conduct themelting operation under a protective flux blanket. A relatively fluidilux is employed for some melting methods,

10% to 15% manganese, up to about 2% silicon, and 0.8% to 1.5% carbon.

7. A container for use in contact with molten magnesium andmagnesium-base alloys which container is composed of a steel containingabout 10% to 30% manganese, chromium'in an amount up to about 18%, andthe remainder principally iron.

8. A container for use incontact with molten magnesium andmagnesium-base alloys which container is composed oi a steel containingabout 10% to 25% manganese, about 5% to 15%, chromium, up to about 2%silicon, up to about 2% columbium, up to about 1% copper, up to about 2%molybdenum, nitrogen in an amount not exceeding about 0.15%, theremainder substantially all iron and incidental impurities includingnickel, the nickel content not exceeding 3%,.

RUSSELL FRANKS. WILLIAM O. BINDER.

